The suburbs don't really do trendy, but here are the places I think have good food and qualify as romantic:
Stained glass (Evanston): nice room, good food, and an excellent wine program. If flights of wine would be a plus, this could be the place.
Oceanique (Evanston): top notch seafood, nice room.
Michaels (Winnetka): old style french cooking with lots of great sauces, and I suspect lots of butter and cream in them; my one meal there was lick your plate good.
Jacky's Bistro (Evanston): The name says it all; French bistro style cooking.
Carlos (Highwood): Very high end. Been around for years. I've not been, so I can't say much about it.
Chef's Station (Evanston): This would be the place if you want a multi-course tasting menu.